Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing the new design.

Within the drawing, the dashed lines that show the display screen or portion thereof form no part of the claimed design. The dashed lines that show portions of the graphical user interface form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 